<?php

$str="在H3PO4溶液中存在下列有关组分，哪一组是共轭酸碱对     ";
$str="    A. CH3COCH3       B. CH2＝CHCl       C. CH2＝CHCH＝CH2   ";
preg_match_all("/[A-Z][a-z]?\d*|\((?:[^()]*(?:\(.*\))?[^()]*)+\)\d+/",$str,$math);

print_r($math);